The majority of lithium ion batteries use a mix of alkyl carbonate based liquid solvents containing a lithium salt as electrolytes. These solvents when used in conjunction with a lithium salt have the ability to form stable passive films around the anode and cathode, a characteristic essential for smooth and efficient functioning of the battery. However, these electrolytes are highly reactive and flammable, and therefore potentially unsafe. Thus, the batteries employing such electrolytes can catch fire or explode especially when overcharged or subjected to temperatures exceeding 125° C. to 130° C.
Given the above, it would be desirable that an alternate electrolyte solvent be found that could provide safer lithium ion batteries. One possible alternative electrolyte solvent disclosed in various publications is a silicone polyether. These solvents have very high flash points (usually above 250° C.) and possess much better flame-retardant properties compared to the alkyl carbonate solvents commonly utilized in lithium batteries.
One of the disadvantages with organic polymer compositions with respect to their usage in Li ion batteries is that such compositions in general have extremely poor ionic conductivities (about 10−14 S/cm) due to the low mobility of the ionic species in such systems. One possible solution was discussed by Wright (see, e.g., P. V. Wright; Polymer; 1973; 14; p. 589) who found that polyethylene oxides (PEO) possess several orders of magnitude greater ionic conductivities (about 10−6 S/cm) compared to other solid polymers. This increase in conductivity was explained by the ability of the polyethylene oxide chains in the polymer to transfer lithium ions. The transfer occurs by chain hopping, which is facilitated by a high degree of segmental motion of polyethylene oxide chains. The preparation of secondary lithium ion batteries employing such compounds as an electrolyte was proposed by Armand et al. (see, e.g., Armand et al.; Second International Conference on Solid Electrolytes; St. Andrews, UK; 20th to 22 Sep. 1978; Paper 6.5).
Given the disclosure contained in these two publications, it was shown that a polyethylene oxide (PEO) complexed with an alkali metal salt can act as an ionic conductor but its ionic conductivity was too low (about 10−6 S/cm) at room temperature for use in any practical application. This was mainly attributed to PEO crystallinity.
With regard to alkyl carbonate-based electrolytes used in lithium ion batteries, these compounds typically have ionic conductivities in the 10−3 S/cm to 10−2 S/cm range. One major requirement in lithium ion batteries, especially in order to achieve a high power density, has been to achieve an ionic conductivity greater than 10−3 S/cm at room temperature (i.e., about 25° C.). Although silicone polyethers have been studied for over two decades as possible electrolyte solvent candidates for lithium ion batteries to achieve this performance level the majority of these polyethers have ionic conductivities that are less than 10−3 S/cm.
Turning to United States Patent Application Publication No. 2009/0035656, this publication discloses a siloxane composition that contains a glycidyl ether functionality. One of the compounds disclosed in this publication is a silane alkoxy glycidyl ether (e.g., dimethoxy or diethoxy silane glycidyl ether as shown in Formula (I) below). No ionic conductivity data is reported in the patent. Coin cell tests done using a lithium salt (1M LiClO4) dissolved in this solvent reports a 69% charge discharge efficiency.

Turning to U.S. Pat. No. 7,695,860, this patent discloses siloxane polyether electrolytes with the polyether appended on the siloxane chain without a spacer. Such electrolytes are stated to provide higher ionic conductivities when compared to those with a spacer. The general formula for such compounds is illustrated below in Formula (II) where n and m are numbers (whole or fractional) that represent the number of repeating units as defined in U.S. Pat. No. 7,695,860. In one embodiment (Example 2 of U.S. Pat. No. 7,695,860), n is equal to 7 m is equal to about 6.3; R1, R2, R3, R5, R6, R7, R8, R9 and R10 are all methyl (—CH3) groups; and R4 is selected from a group shown in Formula (III) below where, for example, k is equal to 3.

Turning to United States Patent Application Publication No. 2005/0170254, this publication discloses silicone polyether oligomers (A) blended with silicone alkyl carbonate (B). LiBOB and LiTFSI salts are dissolved in, for example, a mixture of (A)+(B) or (C)+(B) based on the Formulas shown below. The silicone alkyl carbonate is mainly used to enhance the dissolution of the lithium salt in the given solvent. The maximum room temperature ionic conductivity reported in this publication is 0.2×10−3 S/cm.

Turning to U.S. Pat. No. 7,466,539, this patent discloses electrolytes for double layer capacitors based on the following compounds as illustrated in the reactions below.
Accordingly, there is an unresolved need and desire for an electrolyte composition that can be utilized in a lithium-based battery.